Aahh... so its a question of definition then. That's a problem with a question like the one you quoted, there are different ways of interpreting the key terms. It is possible then we might not even disagree about this.
I think all humans have a responsibility to humanity. Just as all members of a community have a responsibility to the community. Corporations, however, are not truly conscious entities. They are made up individual decision makers (sometimes thousands upon thousands of people), who each know their job and only their job. Alas this sometimes leads corporations astray (it is a kind corporate blindness) . Thus when a corporation makes a disastrous decision or series of disastrous decisions, it is rarely due to some evil mastermind, but rather to a series of decision by, perhaps, well meaning people. I think this is a challenge for humanity though, to find a way to make corporations have a conscience (or at least act like they do). Thus I would say that a corporation should have a responsibility to serve, not just its shareholder, but humanity.